The present invention relates to a controlling unit for controlling revolution of auxiliary devices driven by an engine for a machine such as a car.
A conventional auxiliary device driving unit will be described with reference to FIGS. 1 and 2 in which a crank shaft 2 extends from an engine 1, a crank pulley 3 provided at the outer peripheral surface with grooves 3a in which V-belts are wound is connected to the crank shaft 2 by means of a bolt 4. FIG. 2 is a diagram showing a layout of pulleys for auxiliary devices and the crank pulley 3. A rotational force of the crank pulley 3 is transmitted to the auxiliary devices i.e. a water pump 31, a charging generator 32, an oil pump for power-steering 33 and a compressor for air-conditioning 34 through transmitting belts 35a, 35b, 35c.
Generally, revolutional speed of an engine of a car should be applicable at a wide range. Accordingly, a ratio of transmission of speed is so determined that performance of each auxiliary device is satisfactory even when revolution of the engine is low. The ratio of transmitting speed is determined to increase revolutional speed of auxiliary devices e.g. about 1.0-1.2 for the water pump 31, about 2.0-3.0 for the charging generator 32, about 1.0-1.2 for the oil pump 33 and about 1.0-1.3 for the compressor 34.
The revolutional speed of the engine largely depends on the travelling speed of a car. Therefore, a revolutional speed range of each of the auxiliary devices operated at an increased speed ratio becomes extensively broad. Particularly, in a high speed region, efficiency of operations decreases while consumption horsepower increases, whereby a ratio of travelling distance to a specified amount of fuel (hereinbelow referred to as a fuel ratio) and dynamic performance of the car decreases. Namely, as shown in FIG. 3 showing relations of work per a unit time (hereinbelow referred to as power) and consumption horsepower of each of the auxiliary devices to revolutional speed of an engine, the power output is maximum when the revolutional speed of the engine reaches a certain value, while the consumption horsepower increases at a substantially constant rate. Accordingly, the efficiency of operation is extremely reduced in a high speed region.